This invention relates to plier tools and more particularly to that class of plier tool which is especially suited for use with three wire insulated electrical cable and a process of severing such cable.
Three wire insulated electrical cables such as those sold under the trademark Romex are now widely used for many applications such as distributing electricity in residential units. These cables include spaced positive and negative insulated conductors with a ground conductor wire disposed between them. In copending application for Pat. Ser. No. 09/185,493 filed Nov. 3, 1998 a tool and method for stripping sheathing from the wires is disclosed. While the tool and process taught in that Application have greatly improved and simplified the preparation of an end section of a three wire cable for connection to an electrical device such as a switch or light fixture their remains a problem in that cutting such cables to length is difficult and requires high force. The need for high force occurs in part because with a conventional plier type cutting tool an operator is attempting to cut through all three wires at the same time during a substantial portion of the cutting operation. Accordingly, it would be desirable to provide a plier tool which is effective to sever three wire cables with substantially reduced force.
The orientation of cutting edges of conventional cutter has been found to be a further reason that high forces are required. With typical wire cutters, cooperating cutting edges are each located in an imaginary plane including the pivot axis of the cutting levers. As a consequence forces applied to a cylindrical wire being cut include vectors tending to push the wire away from the cutter""s pivot and thus out from between the cutter edges. Force wasted in these outward vectors result in a higher total force being needed to effect a closure of the cutting tool and severance of a wire. Moreover, some amount of force must be applied to the wire being cut to resist its being urged out from between the cutter edges. Expressed another way, the straight cutter edges of the prior art induce forces that tend to push the wire away from the pivot, thus decreasing the mechanical leverage and increasing the force need to effect cutting.
The tool of the present invention comprises a pair of levers with pivotally connected boss sections. Each of the levers has a handle section projecting in one direction from the boss section and a jaw section projecting in the opposite direction such that the handles and the jaws are respectively coactable.
With the tool of the present invention coacting stepped, non parallel cutter blades are provided in the jaw sections. Each blade has three interconnected parts respectively for cutting the three wires of a Romex type cable. A central one of the three parts is offset from an end part which is nearest the plier pivot. The offset in a direction which is transverse to the jaws cutting action. The third part which is remote from the pivot and substantially adjacent to central part is offset from the central part transversely of the tool such that three parts are of a stepped configuration.
One of the outstanding of the features of the invention is that cutting edges of each of the pairs of cutting parts are oriented such that they are either parallel or canted outwardly in the direction toward the pivot. In contrast to the prior art the cutting edges do not tend to push a wire being cut away from the pivot but rather exert all forces radially of the wire or apply forces such that the cutter edges tend to push the wire being cut toward the pivot. To accomplish this orientation, the edges of each pair of cutter parts are other than parallel to corresponding edges of the other two cutting parts so that as the tool is closed successively on the three wires the cutting forces applied to each of the wires being cut are either radial or include a vector tending to push the wire being cut toward the pivot. This cutter edge orientation results in a significant reduction in the forces required to effect cutting.
The inward angling of the cutter parts minimizes the opening span needed to cut a cable of the type a tool is designed to cut. Since the opening is minimized, so to is the spreading of the handles which contributes to comfortable positioning of the handles when cuts are being initiated. Further, the described orientation of the cutting edges results in the cutter parts each being closer to the pivot axis than the respective parts of a prior art blade cutting the same three wire cable. Thus reducing the arc of travel during a cutting operation. Since the amount of arc travel is reduced so to is the overall handle span from full open to fully closed with the consequence that the handle span is within a comfortable range for a user.
The transverse offset and orientation of the blade parts enables the sequential cutting of the three wires of a cable of a size the tool is designed to cut. In the preferred arrangement a first of the conductive wires will be about 80 percent severed by the cutter parts nearest the pivot before the central part commences to cut the ground conductor. In turn the ground conductor will be about 80 percent severed and the first conductor fully severed when the cutter part remote from the pivot commences to sever the second conductor. Tests on each standard size Romex type cable have shown forces required to cut a cable are reduced from 33 to 40 percent as compared with good quality prior art three wire cable cutters. Moreover this tool is also effective to cut European type cables with corresponding force reductions.
Accordingly, the objects of the invention are to provide a novel and improved plier tool for severing multiwire cable and a process of severing such cable.